from Doug Adams will do the job...mostly.
(Recent changes to iTunes caused a small breakage; dunno if anyone's applied an official patch. I made two small changes and it works great for me. In case you need 'em:
-- replace if thisPlaylist is library playlist 1 then
with if thisPlaylist is user playlist "Music" of source "Library" then
-- at the bottom of the script, in the alert_user_and_cancel()
subroutine, add this line just before "end tell": error number -128